1. Field of the Invention
Apparatuses consistent with the present invention relate to an ultra wide band (UWB) antenna with a unidirectional radiation pattern, and particularly, to a UWB antenna with a unidirectional radiation pattern which mainly performs radiation perpendicular to an antenna plane.
2. Description of the Related Art
In general, a communications system uses a frequency of a particular band to transmit data. Circuit data and packet data are data used in a communications system.
Circuit data are data such as a voice signal for real-time transmission/reception. Packet data are more than a certain size and does not necessarily need real-time transmission.
A frequency band used to transmit the circuit data is usually narrow. To transmit the packet data, a frequency band wider than that of the circuit data is needed.
As described above, as an amount of data transmission increases, the wider a frequency band is needed. A wide frequency band is called a UWB.
The UWB is divided into plural sub-band frequency bands. A UWB communications system transmits data using the plural sub-band frequency bands so that a large amount of data per time can be transmitted.
In addition, a UWB communications system selects one of plural sub-band frequency bands and transmits data through the sub-band frequency band, so that data security can increase. That is, as the plural sub-band frequency bands are used sequentially, data security increases.
FIG. 1 shows frequency bands used in a UWB communications system.
Referring to FIG. 1, frequency bands used in the UWB communications system range from 3432 MHz to 10032 MHz. The UWB frequency bands are divided into four groups of A˜D. There are three sub-band frequency bands for group A, two sub-band frequency bands for group B, four sub-band frequency bands for group C, and four sub-band frequency bands for group D.
The reference frequencies of three sub-band frequency bands for group A are 3432 MHz, 3960 MHz and 4488 MHz, the reference frequencies of two sub-band frequency bands for group B are 5016 MHz and 5808 MHz, the reference frequencies of four sub-band frequency bands for group C are 6336 MHz, 6864 MHz, 7392 MHz and 7920 MHz, and four sub-band frequency bands for group D are 8448 MHz, 8976 MHz, 9504 MHz and 10032 MHz. The sub-band frequency bands for group B are the same as frequency bands used in a wireless LAN, and the sub-band frequency bands for group D can not be used in the present technology level.
FIG. 2 is a schematic view of an antenna suggested to be used in a conventional UWB communications system.
In FIG. 2, the antenna is a wideband antenna with a U-slot, and forms a resonance structure between a radiator, formed at both sides of a substrate, and a ground plane in which radiation occurs at both sides of a patch.
A wideband antenna with a U-slot is cost-effective and can obtain a gain of 5˜7 dB in one direction on the basis of the ground plane. However, a wideband antenna with U-slot has a narrower bandwidth than a bandwidth used in a UWB communications system.
Additionally, U.S. Pat. No. 6,642,903 discusses a method of implementing a wideband by forming a wide plane conductor in a wire dipole which is a narrowband antenna.
The antenna disclosed in U.S. Pat. No. 6,642,903 maximizes radiation perpendicular to a substrate in a low frequency, maximizes radiation on the substrate in a high frequency, and comparatively has a same-directional radiation pattern. However, a directional radiation pattern can not be obtained due to having a small-sized antenna.
In addition, Koshelev, et. al., “Ultrawideband radiators of high-power pulses,” in Proc. IEEE Int. Pulsed Power Plasma Science Conf. #2, pp. 1661-1664, 2001 obtains directivity of the right direction by the combination of an electric antenna and a magnetic antenna.
That is, Koshelev, et. al. can obtain a large gain of 5 dB or more in front, but the size of the antenna is large and power feeding has to be performed perpendicularly behind the antenna.